Submerged Clarifier Launder

ABSTRACT

A clarifier in a wastewater treatment plant is provided with a submerged launder for effluent, the launder preferably having an integral density current baffle and scum baffle. In one embodiment an existing launder is modified, with its vertical leg replaced with a sloped plate defining launder conduit triangular in cross section, and with a sloping portion of the plate forming a density current baffle. Openings in the sloped plate permit entry of effluent liquid, and the liquid level in a clarifier is controlled without an overflow weir plate. In another form submerged pipe with entry holes serves as the launder, with support brackets integral with a density current baffle. A third form of the launder is a box formed beneath the shelf of an existing internal launder in the clarifier, again with a density current baffle extending down from the box. In another version an existing launder is covered and sealed, and holes are drilled through the launder wall to admit effluent. A submerged launder avoids problems of algae buildup and the need for algae sweeps or frequent cleaning of the launder.

BACKGROUND OF THE INVENTION

This invention concerns wastewater treatment plants, particularlyclarifiers, and is directed to an improved clarifier launderconstruction that eliminates algae buildup and the need for algaesweeps, launder covers or frequent cleaning.

Clarifier launders typically are formed by a shelf of concrete, L-shapedin cross section and integral with the wall, on the inside or theoutside of the clarifier wall. They can also be of other materials suchas steel or FRP (fiberglass reinforced plastic). If inside, theconventional launder provides with its vertical leg a weir for overflowof effluent liquid into the launder with a weir plate attached to thetop of the vertical leg. In an external concrete launder the top edge ofthe clarifier with weir plate attached provides the overflow weir.

Algae growth is a recurrent problem in conventional clarifier effluentlaunders. The launders are exposed to daylight, promoting algae growth,and must be cleaned frequently to remove the algae growth. Sometimeseffluent launder algae sweeps have been installed, at significantcapital and operational costs. Without these sweeps, plant operatorsmust frequently clean the launders. In some cases effluent laundercovers have been used to eliminate light and prevent algae growth.

The following documents have some relevance to the current invention:U.S. Pat. Nos. 8,220,644, 8,083,075, 7,416,662, 7,243,802, 6,712,222,6,193,888, 5,597,483, 5,252,205, 5,277,077, 4,059,529 and 4,009,106,U.S. Pub. No. 2012/0248036 and British Patent No. GB 2115304. Of thesereferences, U.S. Pat. No. 8,220,644, shows a somewhat typical inboardlaunder construction with density current baffle and scum baffle.

SUMMARY OF THE INVENTION

The present invention differs from previously known solutions to theseproblems by eliminating costs associated with effluent launders, weirplates and scum baffle plates, launder covers and/or algae sweeps. Thecurrent design requires fewer components to perform the same functions,while also eliminating the problem of algae buildup that requiredperiodic cleaning of the launders by plant operators or continualcleaning by algae sweeps installed in the launders.

In one preferred form the submerged effluent launder of the inventioncomprises a modified density current baffle. A density current baffle inconventional construction is typically attached to the clarifier tankwall about one-half to two-thirds of the side water depth from the tankfloor or to the bottom corner of the launder. In conversion of thedensity current baffle to a submerged effluent launder in thisembodiment of the invention, the inwardly/downwardly angled densitycurrent baffle is extended and elevated such that the highest point ofthe angled plate is attached to the tank wall below the clarifier liquidlevel. A vertical mounting plate at top of the angled plate extends upto or above liquid level and is attached to the wall. Also, the densitycurrent baffle is modified by adding a horizontal shelf that extendsfrom the clarifier tank wall to the inside of the density currentbaffle, thus defining a triangular cross section submerged effluentlaunder. Orifices are formed in the angled wall of the density currentbaffle, at an elevation below the liquid level and preferably just abovethe horizontal shelf of the submerged launder. The submerged effluentexit minimizes or eliminates sun exposure and prevents algae growth.

In another embodiment a clarifier with existing internal launder ismodified by removing the vertical leg of the L-shaped launder, and theremaining shelf becomes the bottom horizontal leg of the triangularcross section launder as described above. Brackets secure the angledlaunder top/density current baffle to the clarifier wall at top and tothe edge of the shelf.

The submerged effluent launder operates hydraulically as a substantiallyor completely full conduit, with liquid level in the clarifiercontrolled by monitoring plant influent flow rate or monitoring liquidlevel in the clarifier and controlling the level by an automatic weirelsewhere in the launder, or by an automatic valve in the effluent pipe.For all iterations of the submerged effluent launder a levelmonitoring/control system must be in place. An example of this is bymonitoring the flow into the clarifier and adjusting an effluent weir orvalve. Another example of this is to have sensors monitoring the liquidlevel that again would adjust an effluent weir or valve to control waterlevel elevations.

Accordingly, the submerged clarifier launder of the invention can be inseveral forms, some of which involve an existing internal launder andothers not, such as in new construction. One embodiment employs asubmerged pipe with openings that admit effluent, the pipe secured to amounting structure that includes a density current baffle. The need fora scum baffle is eliminated in most cases, in that the liquid exits notover a weir but via submerged openings into the launder, while scumremains on the liquid surface.

Significant construction and maintenance costs are eliminated with thesubmerged clarifier launder embodiments of the invention, and the algaebuildup problem is overcome. These and other objects, advantages andfeatures of the invention will be apparent from the followingdescription of a preferred embodiment, considered along with theaccompanying drawings.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross section in elevation showing an outerportion of a clarifier modified according to one embodiment of theinvention.

FIG. 2 is a perspective view with a cross-sectional cut showing anotherembodiment of the invention.

FIG. 3 is a schematic section view similar to FIG. 1, showing a thirdembodiment of the invention.

FIG. 4 is a section view similar to FIG. 1, showing a fourth embodimentof the invention.

FIG. 5 is a perspective view with a sectional cut, showing theembodiment of FIG. 4 applied to a clarifier with an existing launder.

FIG. 6 is a section view similar to FIG. 1, showing a further embodimentof a submerged effluent launder.

FIG. 6A is a section view similar to FIG. 6, with a variation.

FIGS. 7 and 8 are schematic plan and elevation views showing anotherembodiment.

DESCRIPTION OF PREFERRED EMBODIMENTS

FIG. 1 shows an existing clarifier 10, typically of concrete butpossibly of other material such as steel, in a partial cross section,including the outer wall 12 of the clarifier and a portion of theclarifier floor 14. The clarifier had an existing internal launder, butthe vertical leg of the launder has been removed, leaving the horizontalshelf 16. This form of the invention replaces the conventional launderwith a submerged effluent launder 18. The launder is formed as ahydraulic conduit 20 triangular in cross section as indicated in thisschematic drawing. Liquid level of the clarifier is approximately at 22,and freely contacts the outside surface of an obliquely angled plate 24forming the upper side of the new launder. A scum baffle 26 would beimplemented as shown in the drawing, supported by intermittent bafflesupport brackets 28. In another implementation of the invention theliquid level can be lower.

The plate 24 preferably comprises an integral plate that includes adownwardly/inwardly sloping density current baffle 30, as shown.Proportions can be different than illustrated in FIG. 1; the densitycurrent baffle 30 can extend down farther if desired. The lower end ofthe baffle 30 may include an angled lip 32. The upper end of the plate24 may include an extended vertical mounting plate 34 which allows theclarifier to operate at the original liquid level 22. In this scenariothe scum baffle 26 can be eliminated, and the upper vertical plate 34can act as a smooth surface for typical neoprene skimmers to removescum.

The plate unit 24 extends around the entire periphery of the clarifier,assembled in sections. It is attached via integral vertical andhorizontal plates indicated at 34 and 36, to the wall and shelf of theclarifier, using bolts such as indicated at 38 and 40. Access to theshelf bolt 40 would be difficult or impossible, but effluent holes intothe launder are provided through the plate at 42. These can be, forexample, two inch diameter holes through the plate, approximately two tothree inches above the shelf, spaced at 30 inches from hole to hole.Each shelf bolt 40 is at the same position as the effluent hole 42, sothat tool access to the bolt 40 is provided, for securing the brackets36.

Preferably a vent hole is included near the top of the plate,approximately at the position 44 shown in the drawing, so that rising ofthe liquid level inside the launder will not be inhibited. In addition,the vent hole(s) will assist in draining the launder when clarifier istaken down for servicing.

As indicated in FIG. 1, the obliquely angled plate 24 can be at an angleof about 15° to 45° from horizontal.

FIG. 2 shows another embodiment of a triangular cross section effluentlaunder 50 of the invention, installed on the outer wall 52 of aclarifier 54. This form of the invention is adapted for newconstruction, or can be added on the interior of a clarifier wall thathas an existing external launder. In this case the plate at 24 can besimilar to what was described relative to FIG. 1. The plate 24 can bestainless steel or other corrosion resistant metal, or it could befiberglass reinforced plastic (FRP). A shelf 56, which can be of similarmaterial, is installed horizontally as shown between the clarifier wall52 and the under surface of the launder plate 24. As in FIG. 1, thislaunder assembly includes an integral density current baffle 30. Holesfor entry of effluent liquid to the launder are shown at 42, locatedjust above the internal floor of the triangular launder conduit. Thelaunder shelf or bottom 56 can be secured to the plate 24 by appropriatefasteners or by welding, and the shelf can be secured to the clarifierwall via an L-shaped flange on the shelf at the wall. However, theentire launder/density current baffle assembly could be formed as asingle integrally molded unit such as from FRP. Vent hole(s) can beincluded in the plate 24 at a similar position as discussed aboveregarding FIG. 1, for the same purposes stated there.

FIG. 3 shows another variation, on a clarifier 10 a having an existinginternal launder 58 which would be the same as was existing prior to themodifications shown in FIG. 1, including a vertical leg 59. A submergedlaunder in the form of a rectangular box 60 is installed beneath theexisting launder shelf 16. The box can comprise simply an L-shapedattachment, but preferably also including a density current baffle 62 asshown. As above, the submerged effluent launder 60 can be integrallyformed of FRP to include the density current baffle 62, or could beformed individually and assembled. The L-shaped portion has an uppermounting bracket 64 and a lower mounting bracket 66, both of which canbe continuous, and the unit is secured to the existing structure insubstantially sealed relationship, as also is the case with forms shownin FIGS. 1 and 2.

A series of liquid entry orifices 68 in the unit 60 are positioned justbelow the existing shelf 16 or at a level as desired in the launderunit. These orifices also serve as vents to facilitate draining whenneeded for service.

FIG. 4 shows another form of the invention, in the form of a submergedeffluent pipe 70 that forms the submerged launder. This form of theinvention, shown also in FIG. 5, can be used on a newly constructedclarifier or on an existing clarifier with an external launder 72, suchas shown in FIG. 5.

The conduit or pipe 70 has orifices positioned as desired, such as atlocations indicated at 74 (which can be about 2 inch diameter) in FIGS.4 and 5. The pipe 70 itself can be, as an example, about 20 inches indiameter for a 100-foot diameter clarifier tank.

This embodiment includes a density current baffle 76, similar to thosediscussed above, but the baffle 76 is a part of a mounting structure 78for the pipe 70. This structure 78 preferably is continuous from theclarifier wall 80 to the lower end of the baffle 76, for function as adensity current baffle, which should not allow throughflow except thatvents can be included at the top of the density current baffle (near thewall 80) to prevent gas buildup. This structure is secured to theclarifier wall by bolts as indicated at 81, and includes or supports apipe saddle 82 that firmly retains the pipe 70 to the mounting structure78. One or more vent holes preferably are located at top of the pipe sothat a rising level of liquid inside the launder will not be inhibited,and the vent will facilitate draining the launder pipe when taken downfor service.

In this form of submerged launder, a gap may be provided between thepipe 70 and the angled platform structure 78, to allow the settlingsolids to pass through and slide down the angled platform 78.

FIG. 6 shows another embodiment of the invention, with a retrofittedsubmerged effluent launder shown at 85. This is an adaptation of anexisting internal launder of a clarifier, typically of concrete,including a horizontal shelf 16 and vertical leg 59 that defined theexisting launder along with the external clarifier wall 12.

In this form of submerged launder of the invention a top plate 86 isaffixed at the top of the existing launder as shown, in sealedrelationship. Typically neoprene material is engaged between the cover86 and the existing concrete surfaces (and the same or similar sealingmaterial can be used for sealing purposes in the earlier-describedembodiments). The plate preferably is angled as shown, declininginwardly so as not to trap rain, etc. The top plate 86 forms a closedconduit, i.e. a fully or partly submerged effluent launder, preferablypositioned about at or close to the liquid surface 22 in the clarifier.At least part of the launder must be submerged. As shown, the addedplate 86 can have vertical plates, preferably integral, at both innerand outer sides. At the outer side is a continuous plate or flange 88that engages with the tank wall 12, for bolting at intervals to thewall, and at the inner side is a depending plate 90 that laps over andagainst the existing concrete launder leg 59. This vertical plate 90provides a closure, provides for affixing the top plate to the leg viabolts 91, and also acts an integral scum surface, i.e. a smooth surfacefor the skimming mechanism to ride against in order to efficientlyremove scum from the surface. The preferred clarifier liquid level isindicated at 22, and the plate 90 preferably extends about four inchesabove the existing liquid level.

Effluent liquid enters the launder 85 via openings 92 through thevertical leg 59 as shown. These orifices can be about 2 inches indiameter, for example, formed by drilling, and spaced apart atappropriate intervals such as every 2 to 3 feet, depending in part onorifice size. The depth location of the orifices 92 can vary, and theorifices could be through the bottom 16, but that is not preferred.

The plate or flange 88 at the upper/outer end of the sloped top cover 86provides for mounting that side of the cover plate 86 to the clarifierwall 12 (with bolts 94). A vent orifice 96 can be formed (at intervals)through the plate 86 near the upper side, the orifice oriented at anangle (up and to right in the drawing) so that any sunlight will onlyenter high in the launder. A downwardly extending vertical plate 98 canbe included, extending down against the wall 12, for any sunlightcontact. The plate if a smooth surface of FRP discourages algae growth.

In this embodiment the launder 85 will typically be partially submergedin the clarifier, not fully. The liquid level in the clarifier (and inthe launder) can be about as shown so that the surface 90 acts as a scumcleaning surface. In all forms of the invention the launder is fully orpartially submerged. The forms shown in FIGS. 1-5 can be fullysubmerged, or submerged at least to the extent that the effluent isevacuated efficiently and the effluent openings are submerged far enoughthat sunlight will not be able to encourage algae growth. Typically thisshould be roughly 16 inches to 20 inches below the clarifier liquidsurface. In all embodiments the launder should be at least about 50%submerged, based on the internal height of the launder.

FIG. 6A shows a variation of FIG. 6, in which an effluent inspectioncover 99 is included in the top plate 86. This hinged viewer port plate,which can be up to a few feet wide, is only needed at one location. Itcan be provided in one section of many assembled sections that form thelaunder.

Note that the FIG. 6 embodiment can also be applied to an existingexternal launder, with effluent entry holes drilled through theclarifier wall.

FIGS. 7 and 8 are schematic illustrations for another embodiment ofsubmerged clarifier effluent launder of the invention. FIG. 7 is apartial plan view showing a clarifier tank wall 100 with an effluentlaunder 102 positioned inside the launder. This can be a retrofit for anexisting clarifier launder consisting of an open launder positionedinward from the clarifier wall, e.g. 15 or 16 feet in from the wall of a100 foot diameter clarifier, wherein the effluent launder entered thewater from weirs at one or both sides of the launder. Such an integrallyspaced launder, circular like the clarifier wall, has been supported bycantilever beams extending inward from the clarifier wall (e.g. ofreinforced concrete). In the invention an open weir-type launder isreplaced by the submerged pipe 102, which can be like the wall-mountedembodiment of FIG. 4 in some respects.

The submerged pipe launder 102, as shown in FIGS. 7 and 8, collectseffluent from below the surface and delivers the effluent through alateral exit pipe 104, preferably having a control valve 106, and thenthrough an open channel 108 to exit the clarifier. For admittingeffluent the pipe 102 has orifices indicated schematically at 110 inFIG. 8, preferably located at the lower half of the pipe, e.g. at alocation about 30° from the pipe bottom. The orifice can be, forexample, 2″ to 2½″ in diameter. The effluent launder pipe 102 issupported on a beam 112 that extends inward from the tank wall 100,these cantilever support beams being spaced at appropriate intervalsaround the clarifier. The withdrawal pipe or conduit 104 carrieseffluent from the launder 102, through the control valve 106 thenthrough the channel 108, which preferably is an open channel for viewingthe effluent as it exits the clarifier. Plant operators often inspectthe quality of the effluent of the clarifier, and this is convenientlydone with the viewing channel 108. The exit pipe 104 and channel 108need be provided only at one location around the clarifier'scircumference. Although the open channel 108 will be subject to algaeaccumulation, it will only be of short length, for example about 5 feet,and can easily be cleaned from the tank wall.

The open channel 108 has another purpose as well; the maximum designliquid level is shown at 22 in the drawing, with the sides of the openchannel 108 being an inch or two higher than the maximum liquid level.This provides an overflow to withdraw clarifier water in the event of afailure in the system, such as failure of the valve 106 (which is anautomatically controlled valve) to allow the proper amount of effluentout of the clarifier. The clarifier liquid level will then rise beyondthe design level 22, but would flow into the open channel 108 forwithdrawal.

It should be understood that the effluent viewer channel 108 can beprovided outside the clarifier instead of inside the clarifier, and canbe included with the other embodiments. For example, an open channelsuch as that shown at 108 can be just outside the clarifier tank wall,receiving effluent that has been collected any of the laundersdescribed. The open channel allows inspection such as by an operator onthe top of the tank wall. An automatic control valve can be downstreamof the open channel, and if that level control valve should fail, theopen channel, with its walls an inch or two above maximum design liquidlevel, would overflow outwardly. A basin below the channel can catch theoverflow and can conduct it through a pipe to join the rest of theeffluent, at a lower elevation. Note that if the viewer channel is notto serve also as an emergency overflow weir, it can have a removablecover, or it could be covered but with an openable viewing port.

The several embodiments of submerged clarifier launders described aboveeliminated algae problems, the cost of cleaning or algae sweeps, andreduce capital expense in forming a conventional clarifier launder in anewly-constructed clarifier.

The above described preferred embodiments are intended to illustrate theprinciples of the invention, but not to limit its scope. Otherembodiments and variations to these preferred embodiments will beapparent to those skilled in the art and may be made without departingfrom the spirit and scope of the invention as defined in the followingclaims.

We claim:
 1. In a wastewater treatment clarifier having an effluentlaunder for withdrawal of effluent from the clarifier, the improvementcomprising: the clarifier having a peripheral clarifier wall, and thelaunder being secured to the inside of the clarifier wall, the launderbeing at least partly submerged below the liquid level in the clarifier,and the launder having inlet orifices submerged below the liquid levelof the clarifier.
 2. The improvement described in claim 1, furtherincluding a density current baffle extending downwardly and inwardly inthe clarifier and being formed as part of the launder.
 3. Theimprovement described in claim 1, wherein the submerged effluent launderis formed by modification of an existing internal launder of theclarifier, with a vertical leg of the existing launder removed and thesubmerged launder formed on a remaining horizontal shelf of the existinglaunder, and the launder comprising an angled plate extending from aninward edge of the horizontal shelf obliquely up to a connection to theclarifier wall, thus forming a submerged launder triangular in crosssection, with said inlet orifices in the obliquely angled plate to admitclarifier effluent liquid.
 4. The improvement described in claim 3,wherein the obliquely angled plate has an integral vertical plate at itsupper end, engaged against the clarifier wall, providing a smoothsurface for scum skimming.
 5. The improvement described in claim 3,wherein a density current baffle is formed as an extension of andintegral to the angled launder plate, extending over and beyond theinward edge of the horizontal shelf.
 6. The improvement described inclaim 1, wherein the submerged launder comprises an inwardly/downwardlyobliquely angled plate connected to the internal side of the clarifierwall as an upper side of the launder, a generally horizontal platesecured to the clarifier wall at a level below the connection of theobliquely angled plate to the wall, the obliquely angled plate beingconnected to an inward side of the generally horizontal plate, at alevel such that the obliquely angled plate extends beyond the generallyhorizontal plate to form a density current baffle for the clarifier, andthe obliquely angled plate having orifices to admit effluent water fromthe clarifier, and the upper side of the launder being approximately ator below a liquid level in the clarifier.
 7. The improvement describedin claim 6, further including vent holes near an upper end of theobliquely angled plate.
 8. The improvement described in claim 6, furtherincluding an integral vertical plate extending up from the upper end ofthe obliquely angled plate, the vertical plate being secured against theclarifier wall with bolts, and the vertical plate extending upsufficiently to form a scum surface, about four inches above the liquidlevel in the clarifier.
 9. The improvement described in claim 1, whereinthe effluent launder is fully submerged and is rectangular in crosssection, secured beneath an existing concrete shelf of an existinginternal launder of the clarifier, with orifices in a wall of thelaunder for admitting effluent liquid into the launder and acting as avent when the launder is drained.
 10. The improvement described in claim9, wherein the submerged launder comprises an attachment L-shaped incross section and secured to the clarifier wall and to the existingconcrete shelf, and having an extension oriented downwardly and inwardlyof the clarifier, as a density current baffle.
 11. The improvementdescribed in claim 1, wherein the effluent launder is fully submergedand comprises a pipe with effluent inlet orifices, and an obliquelyangled plate secured to the inner side of the clarifier wall, the pipebeing secured to the obliquely angled plate and at a position such thatthe plate extends downwardly and inwardly of the clarifier to form thedensity current baffle.
 12. The improvement described in claim 1,wherein the submerged launder is formed on an existing internal launderin a concrete clarifier tank, and comprises a launder plate positionedabove a vertical leg of the existing launder, the plate having an outerside secured against the inside surface of the clarifier wall and aninner side with a downwardly extending vertical plate secured against aninner surface of the existing clarifier leg to form a substantiallyclosed launder conduit of generally rectangular cross sectional shape,the downwardly sloping plate being positioned such that the existingliquid level surface in the clarifier is between upper and lower ends ofthe downwardly extending vertical plate to act as a scum baffle in theclarifier.
 13. The improvement described in claim 12, wherein thelaunder plate forming the top of the launder is angleddownwardly/inwardly of the clarifier.
 14. The improvement described inclaim 12, wherein the launder plate forming the top of the launderfurther includes a small vent opening, and the launder plate including asunlight contact plate extending downwardly along the inside of theclarifier wall so that any sunlight penetrating through the vent openingwill contact the sunlight plate.
 15. The improvement described in claim14, wherein the sunlight plate is of smooth FRP.
 16. The improvementdescribed in claim 1, wherein the effluent launder is fully submergedand comprises a pipe with effluent inlet orifices, the pipe being spacedinward of the clarifier wall and supported on cantilevered beams fromthe clarifier wall, and including a lateral effluent withdrawal pipeconnected to the effluent launder and extending to exterior of theclarifier.
 17. A method for converting a clarifier of a wastewatertreatment system having an interior concrete effluent launder on theclarifier wall, generally L-shaped in cross section with a horizontalshelf and a vertical leg, to a submerged effluent launder, comprising:removing the vertical leg of the launder, throughout the circumferenceof the clarifier, and attaching an obliquely angled plate onto theclarifier, to extend from an inward edge of the horizontal shelfobliquely up to a connection to the clarifier wall to thereby form asubmerged launder triangular in cross section, and including orifices inthe angled plate to admit clarifier effluent liquid, the launder beingat least mostly submerged in the liquid of the clarifier.
 18. The methodof claim 17, wherein the obliquely angled plate has an integral verticalplate at its upper end, and including securing the integral verticalplate against the clarifier using bolts, to retain the obliquely angledplate and to provide a smooth surface for scum skimming.
 19. The methodof claim 17, further including providing a density current baffle as anextension of and integral to the obliquely angled plate, to extend overand beyond the inward edge of the horizontal shelf.